Psoriasis

Chronic immune-mediated inflammatory skin disorder characterized by clearly defined, erythematous and scaly plaques.

• Common (≈2% of people) and not just skin-deep: psoriasis is a multisystem inflammatory disease that significantly impacts quality of life. Associated with comorbidities like psoriatic arthritis, metabolic syndrome, cardiovascular disease, inflammatory bowel disease, and depression, and severe flares (e.g. pustular, erythrodermic) can be life-threatening.

• Plaque psoriasis (most common): Well-demarcated red plaques with silvery-white scale, usually on extensor surfaces (elbows, knees, scalp); often symmetric, sometimes with itch.
• Guttate psoriasis: Widespread small teardrop-shaped papules with fine scale, often acute onset after streptococcal throat infection (younger patients).
• Inverse (flexural) psoriasis: Involves intertriginous areas (axillae, groin, inframammary); presents as smooth, red, shiny patches with minimal scale in skin folds.
• Pustular psoriasis: Sterile pustules on an erythematous base. Can be localized (e.g. palmoplantar) or generalized (von Zumbusch variant with fever and systemic toxicity). Generalized pustular flares are serious medical emergencies.
• Erythrodermic psoriasis: Diffuse erythema and scaling over most of the body (>80–90% BSA); skin loses its barrier function, leading to risk of hypo-/hyperthermia, infection, and cardiac failure.

1. Diagnosis is usually clinical; a skin biopsy is reserved for atypical or uncertain cases.
2. If biopsied, classic findings include acanthosis (epidermal hyperplasia) with parakeratosis (retained nuclei in stratum corneum) and Munro microabscesses (neutrophil clusters in stratum corneum).
3. Assess disease severity by body surface area (%BSA involved) and impact on patient. <3% BSA is mild, >10% is severe (often requires systemic therapy).
4. Check for triggers or exacerbating factors: recent infections (especially streptococcal), medications (lithium, beta-blockers, antimalarials, steroid withdrawal), and stress.
5. Evaluate for psoriatic arthritis in all psoriasis patients (ask about joint pain/stiffness, examine for nail pitting or onycholysis which often correlate with arthritis).

1. Mild (limited BSA): High-potency topical corticosteroids (± vitamin D analogues like calcipotriene) are first-line; additional options include topical retinoids (tazarotene), calcineurin inhibitors (for inverse areas), coal tar, salicylic acid, and moisturizers.
2. Moderate: Phototherapy (narrowband UVB) is effective for widespread lesions. If phototherapy is unavailable or psoriasis is progressing, use systemic agents (e.g. methotrexate – the most common systemic treatment, or cyclosporine for rapid control, or oral retinoids like acitretin especially for pustular or palmoplantar psoriasis).
3. Severe or refractory (or psoriatic arthritis present): Biologic therapies (monoclonal antibodies targeting TNF-α, IL-17, IL-23, etc.) can induce remission in moderate-to-severe psoriasis. Examples: TNF inhibitors (etanercept, infliximab), IL-17 inhibitors (secukinumab), IL-12/23 or IL-23 inhibitors (ustekinumab, guselkumab). These require screening for latent infections and regular monitoring.
4. Avoid oral corticosteroids in psoriasis flares – while they can temporarily suppress lesions, tapering off can trigger severe rebound flares (pustular or erythrodermic psoriasis).

• Auspitz sign: pinpoint bleeding when a scale is scraped off (due to dilated dermal capillaries).
• Koebner phenomenon: new psoriasis plaques often appear at sites of skin injury or trauma (e.g. scratches, surgery scars).
• Nail involvement (pitting, onycholysis) is common and associated with psoriatic arthritis (if you see nail pitting + joint pain on exams, think psoriasis).

• Erythroderma (generalized >90% skin redness and scaling) in psoriasis – can cause dehydration, hypothermia, high-output cardiac failure; requires hospitalization and urgent dermatologic care.
• Generalized pustular psoriasis – presents with diffuse sterile pustules, fever, leukocytosis; high risk of sepsis and electrolyte imbalances. This is a dermatologic emergency (often ICU-level care).

1. Chronic scaly rash on extensor surfaces → suspect psoriasis; look for well-demarcated plaques with silvery scale and nail changes.
2. Rule out tinea (KOH test) or other mimics if uncertain. If diagnosis is in doubt, perform skin biopsy to confirm psoriasiform changes.
3. Assess severity: determine %BSA (≤3% mild, 3–10% moderate, ≥10% severe) and check for joint involvement (psoriatic arthritis).
4. For mild disease, start topicals (steroids ± vitamin D analogs). For moderate disease, consider phototherapy or add systemic agents (e.g. methotrexate). For severe disease or arthritis, use biologics or combination therapy.
5. Monitor over time for treatment response and manage comorbidities (cardiovascular risk, depression, arthritis) in collaboration with primary care and rheumatology.

• Adult with chronic extensor elbow and knee plaques covered by silvery-white scale, and nail pitting → plaque psoriasis.
• Young patient with dozens of small drop-like scaly lesions erupting after a strep throat infection → guttate psoriasis.